Why Was The Floating Harbour Built?
The town of Bristol grew up around a point on the river Avon six miles inland from where it flows into the Severn Estuary (now called Avonmouth), and from there into the Bristol Channel. Bristol developed at the most downstream point where it was convenient to cross the Avon, and where ships could be carried up to the town’s harbour on the tidal current in the river.
The tidal range of the rivers in the Bristol Channel is the second greatest of any in the world (the biggest is the Bay of Fundy, Nova Scotia, Canada). At Avonmouth the tide can rise and fall as much as 14 metres twice a day and even in Bristol the water level can change as much as 12 metres.
This was both an advantage and a disadvantage for sailing ships. On the plus side, ships could be carried all the way to Bristol on the current before the tide changed. Less helpfully, they would be stranded in the mud when the tide went out. Until the late 1700s, this was not considered too much of a problem, and ships were built that little bit stronger to cope with this.
By the 1760s, however, Bristol was so popular as a destination for cargo ships that it became impossible to accommodate them all. Some ships were beginning to go to other ports like Liverpool where there was more capacity.
There Were Several Problems
- The river was too crowded on each tide with ships trying to reach or leave Bristol.
- On monthly neap tides (when the gravitational pull of the moon creates lower high tides) there was never enough water in the river for larger ships to move, so they would have to wait for a week or two in Bristol or at the mouth of the Avon, further congesting the port.
- At low tide, all the ships in port went aground, crowded together. There was a real danger of a fire starting aboard one ship spreading to all of the others, with no chance of controlling the spread.
- Ships were sometimes stranded in the river on the way to Bristol, causing damage to them.
Merchants in Bristol began to think of ways to make the harbour non-tidal by damming the river. This would allow the ships that were in harbour to stay afloat hence a ‘Floating Harbour’.